Induced Seismicity Risks

Transcription

1 Induced Seismicity Risks Maurice Dusseault

2 Earthquakes Natural Earthquakes Geotectonic Earthquake Ocean Earthquake tsunami Volcanic Eruption Induced Seismicity Tidal Triggering of Earthquake Man-made Earthquakes Underground Nuclear Explosion Related Seismicity Induced Earthquakes ( σ, p, T ) Could O&G development be highly risky?

3 A Review Seismology Fundamentals Exploration Applications Induced Seismicity Resource Management Applications Public Relations Considerations These slides ware from a public PPT file: GRC Exploration Workshop, Sept 28-29, 2007 Earthquake Monitoring. Some modifications were made. Thanks to those who make such things public!!

4 Plate Tectonics DOE Geothermal Website Earthquakes occur primarily along crustal plate boundaries, where the plates move past one another. That s also where geothermal resources are found.

5 How Earthquakes Occur Dr. R. Uhrhammer, UC Berkeley The movement of the Earth's plates deforms the crust at the edges of the plates, stressing the rocks. When the stress exceeds the static frictional force across a fault, the fault ruptures and the rocks are displaced, causing an earthquake.

6 Seismic Wave Generation Dr. R. Uhrhammer, UC Berkeley

7 The Seismograph Detects earthquake ground motions Inertial reference Clock Sensitivity Natural Period Damping Noise This illustrates the principle of seismometer operation. Modern seismometers register motion with a spring-mounted mass that moves inside a coil to induce an electric signal. Dr. R. Uhrhammer, UC Berkeley

8 Locating Earthquakes Dr. R. Uhrhammer, UC Berkeley Earthquakes are located based on timing of seismic wave arrivals at multiple synchronized stations. It s a 3D problem to resolve the hypocenter. The epicenter is the surface projection of the location. Need spread of stations (array aperture) to resolve locations. Poor resolution of earthquakes outside array or for depth > 0.5*aperture.

9 The Richter Scale Distance to Epicenter Maximum Amplitude on Seismogram Logarithmic Scale 10x Amplitude 32x Energy Dr. R. Uhrhammer, UC Berkeley There is no Richter-meter. Magnitude is calculated using measurements from seismograms at a number of stations. After a large earthquake, magnitude estimates will typically jump around as data are gathered and analyzed.

10 Magnitude vs Frequency of Occurrence 5.0 Log cumulative number of events y = -1.4x Extrapolate recurrence rates for largemagnitude quakes Magnitude threshold of seismic network B-slope typically ~1: activity increases tenfold for each unit magnitude decrease Magnitude 10

11 The Modified Mercalli Scale MMI Typical Effects I II III IV V VI Not felt Felt by persons at rest, on upper floors, or favorably placed. Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Windows, dishes, doors rattle. Small unstable objects displaced or upset. Doors swing, close, open. Windows, dishes broken. Books off shelves. Weak plaster cracked. VII Weak chimneys broken at roof line. Fall of loose bricks, stones. Some cracks in masonry C. Waves on ponds; water turbid with mud. Small slides. VIII IX X XI XII Some damage to masonry B, fall of stucco, some masonry walls and chimneys. Frame houses moved on foundations if not bolted down. General panic. Masonry B seriously damaged. Frame structures, if not bolted, shifted off foundations. In alluvial areas sand and mud ejected, earthquake fountains, sand craters. Most masonry and frame structures destroyed. Large landslides. Rails bent greatly. Underground pipelines completely out of service. Damage nearly total. Large rock masses displaced. A descriptive scale of observed effects at a given receptor site. Intensity depends on: earthquake magnitude, distance to epicenter, and local geology

12 Risk Assessment Steps Regional Tectonic Setting Is the area near a plate boundary or other major tectonic feature? What is the rate of slippage across the plate boundary? Faults Map surface faults, with attention to the long ones (10 miles or more). Seismic history Seismologic data: are there small quakes aligned along the fault? Historic (written or oral) accounts of earthquakes in the area. Geologic evidence for recent (last few thousand years) displacement along the faults. Probabilistic Seismic Hazard Assessment Statistically forecast earthquake magnitudes and locations Model or extrapolate effects at receptor communities Forecast recurrence intervals of shaking at receptor communities

13 Reservoir Hot Dry Rock Seismicity

14 Geysers Geothermal - California Geysers Annual Steam Production, Water Injection and Seismicity, E Induced Seismicity Earthquake Risks Count Prior to 1985, seismicity increased along with production and injection 0 0 Largest was magnitude 4.6 in 1972 Since 1985, fieldwide earthquake count (M>3.0) has been stable Fieldwide Count M>=1.5 Fieldwide Count M>=3.0 Steam Production Water Injection SEGEP Startup 2000 SRGRP Startup Steam Production and Water Injection (billion lbs)

15 Seismicity Spread with Development Loch Lomond Loch Lomond Hobergs Hobergs Cobb Forest Lakes Whispering Pines Cobb Forest Lakes Whispering Pines Anderson Springs Eberhart-Phillips and Oppenheimer (1984) noted spread of seismicity as development area expanded, and inferred expanding area of production-induced seismicity. As seismicity spread toward residents, felt effects and community concern increased. Anderson Springs Reservoir Limit (red outer line), microearthquakes (brown dots) and developed areas (multicolored lines)

16 North Geysers Microearthquakes (2002) Activity extends beyond producing wells. Pressure observation data confirm that pressure drawdown extends to these areas. A A' Injection Well Microearthquake Depth Range: km subsea km subsea Scale (km) B B'

17 Geyers Induced Seismicity LF-15 Geysers Injection-Induced Seismicity Local clustering of micro-earthquakes around most injection wells. Timing: seismicity lags injection by days, weeks, or a few months. Generally limited to M<3.0.

18 Geysers Timing of Seismicity Earthquake count LF Monthly injection and NCSN seismicity in area around SRGRP injection well LF-15. Line with circles is monthly water injection. Dashed line is monthly count of earthquakes of M>=1.2. Solid line is monthly count of earthquakes of M>=2.0. x s show maximum magnitude each month injection (mgd) or earthquake magnitude

19 Geysers Spatial Distribution U 9/10 U 9/ LF-15 Area Pre-injection, 8/22/ /21/03 Earthquake Magnitudes SONOMA 4.0 SONOMA LF-15 Area During Injection, 3/1/ /28/ Seismicity maps before and during injection at LF-15. Area shown is 4000 box centered on midpoint of steam of injection well. NCSN seismicity data, magnitudes 1.2. FEET

20 North Geysers Injection and Microearthquakes (2002) A A' Injection Well Microearthquake Depth Range: km subsea km subsea Scale (km) B B'

21 Cross-section B-B showing injection wells and MEQ s

22 This map shows earthquakes recorded by USGS during Over 3,000 were located in The Geysers. Elsewhere, the quakes are concentrated along linear fault zones, such as the Rodgers Creek Maacama faults in Sonoma County and the Bartlett Springs Fault in Lake County.

23 This map shows regional earthquakes of magnitude 4.5 or greater recorded by USGS since Only one was located in The Geysers, and it occurred in Elsewhere, the quakes are again concentrated along the known fault zones. The cluster south of Chico is related to the Oroville Dam.

24 Conclusions Recharge Project SRGRP is likely to increase the incidence of Intensity V shaking events (pictures move, small unstable objects displaced or upset) by approximately 38% SRGRP will have little effect on incidence of Intensity VI shaking events (objects fall, dishes and glassware broken) Maximum magnitude of Geysers induced seismicity tentatively assessed at 5.0 Will not increase the risk of larger earthquakes on nearby faults 24

25 Monitoring, Management, Communication Upgraded seismic network Strong-motion stations All data available to the public on the web. Voic Hotline Injection adjustments to minimize quakes Regular public meetings and newsletters Written report to Santa Rosa every 6 months on the seismic impact of SRGRP injection. Lake County Seismic Monitoring and Advisory Committee (SMAC). Increased funding of community projects

26 Fault Reactivation Pore pressure generation is a major natural trigger for fault motion, particularly thrusting, which needs high pressures The far-field stresses, either normal or tectonic, provide the energy for slip At yield, it is likely that a major valving event occurs along faults (spill-point) Faults may stabilize or be triggered by us Stress change effects are vital as well And what are we doing to change p, σ? These are complex issues

27 Induced Earthquakes Anthropogenically Induced Sources Mining Tunneling Dam Reservoirs Injection ( p, T) Exploitation ( p)

28 Induced Earthquake Distribution [Adushkin, 2000]

29 Injection-Induced Induced Seismicity Injection: p σ, also, V + σ, and T effects σ transfer to faults, fracture zones? Hydraulic fracturing Density-driven loading (gas ) [Sminchalk, 2002]

30 Exploitation-Induced Seismicity p poroelastic stress transfer HC withdrawal isostatic imbalance Regional stress transfer (reservoir scale x 5) Mass transfer and fluid circulation [McGarr, 1991] [Segall, 1989]

31 Identification of Induced Seismicity Spatiotemporal correlation between injectionproduction history and seismicity The relationship between frequency and magnitude of earthquakes (b-value) The relationship between the magnitude of the main shock and maximum aftershocks Magnitude-time decay of after-shocks The model of preshocks and aftershocks

32 Zagros Sedimentary Basin An example of a study in Iran [Alsharhan, 1997]

33 Oil and Gas Fields distribution in Zagros Basin

34 Kuh-e e Mond Heavy Oil NFCR

35 Data Gathering The seismic data were gathered from different source such as International Institute of Earthquake Engineering and Seismology (IIEES) Building and Housing Research Center (BHRC) Institute of Geophysics of University of Tehran (IGUT)

36 Data Analysis

37 Annual seismicity of Zagros Basin (including the Shiraz local seismic network)

38 M 2.0

39 M 3.0

40 M 4.0

41 M 5.0

42 M 6.0

43 Focal Depth 5 km

44 Focal Depth 10 km

45 Focal Depth 20 km

46 Focal Depth 50 km

47 Zagros Region Seismic Parameters Gutenberg-Richter Frequency-Magnitude Distribution (1941) log 10 N = A bm N: cumulative earthquake number with magnitude greater than M A, b: constants (A>0, b>0) A = b = 0.985

48 The b-value b Contour Map Zagros region was divided into different blocks 1 1 degree blocks ( km 2 ) degree blocks (55 55 km 2 ) b-value was calculated for each block

49 b-value Contour Map km 2 blocks

50 b-value Contour Map km 2 blocks

51 Case Study: Oil Field B Field: 65 by 8 km 2 Discovery: 1928 Production: 1937 Injection: 1977 Cumulative (2001) 8.34 BBL Oil 4.35 TCF Gas Injection Rate (2001) 6.13 TCF Gas

52 Seismicity of Oil Field B

53 Seismicity & Fault Location

54 Seismicity vs. Injection & Production

55 Conclusions 2674 earthquakes (0.3<M L <6) in the Zagros region were gathered. Uncertainty remains in event locations (z) Contours of b-values at different scales 1 1 degree blocks ( km 2 ) degree blocks (55 55 km 2 ) b-value contour maps indicate active regions, suitable areas for more detailed investigations Oilfield B: most seismicity increase in 1976, 1983, 1989 induced by injection, exploitation

56 Recommendation Local seismic networks on Iranian O&G fields are advised for several reasons assess risk of induced seismicity obtain more information dynamic behavior of reservoirs geology and use as a source functions to help refine the velocity models potentially, tracking processes over time Large-scale damaging earthquakes seem highly unlikely from O&G activity

57 Overall Issues Seismic risk assessment in O&G requires: Historical and background data A commitment to monitoring locally A sufficient system of sensors, reasonable analysis In many regions, stress criticality exists In general, risks of generating a large and destructive earthquake are small Stressed volumes are small Depths are shallow (local shaking) But, monitoring, coupled analyses are vital